1. Field of the Invention
The invention relates to a rolling bearing arrangement for a rotational connection for the purpose of relative movement of a plurality of at least two rotating elements supported against each other; in particular, rolling bearing rings supported against each other, at least one rolling element raceway being hardened along its annular shape in a contact area between rolling element and rolling bearing ring.
2. Description of the Prior Art
In the prior art, raceway hardening is often envisaged for rolling bearing rings in order to increase the load capacity, and thus the service life, of a rolling bearing arrangement for a rotational connection. One technique known is the use of continuous annealing furnaces, in which the workpieces to be hardened, for example, rolling bearing rings, pass through an apparatus in the longitudinal direction and are thereby heated such that only certain subregions of the particular rolling bearing ring are hardened. One of the most commonly used methods of raceway hardening is inductive hardening. In this process, inductors, or induction heads, are moved relative to a ring to be hardened, a raceway to be hardened, or a portion of the rolling bearing ring.
Patent document DE 10 2007 014 637 A1 discloses such an apparatus for the inductive heating of at least surface layers of an annular workpiece. The inductors, or induction heads, are movable, at least with respect to their radial distances from one another.
WO 2010/007635 A1 and EP 1 988 179 A2 also describe methods and devices by means of which subregions of raceways of rolling element rings can be inductively hardened. These inventions employ at least two inductors, or induction heads, which are brought to a preset distance from the surface to be hardened, while a workpiece to be hardened and the inductors move relative to one another. Finally, DE 10 2005 006 701 B3 further discloses a method for producing a bearing ring for large rolling bearings that operates on a basically similar principle.
A so-called “hardness gap” can also be an important factor in the practical installation of such rotational connections. “Hardness gap” is the term for the discontinuity between the beginning and the end of the raceway hardening. In practice, this is the location that undergoes little or no hardening during the process of hardening the raceway, particularly during the inductive hardening process. In the current state of this technology, almost all rolling bearing arrangements have such a hardness gap region.
JP 2002 174 251 A shows, in principle, and by way of example, a specially dimensioned such region surrounding the hardness gap, depicted as a window-like section extending along a rolling element raceway disposed between two adjacent hardened regions.
This location is usually of lower hardness than the surrounding hardened material. Less-hard regions of the raceway usually present disadvantages for the rolling behavior of the rolling elements, since the load capacity in less-hard sections of the raceway is lower than in the hardened raceway sections.
In addition, many rolling bearing arrangements, for example, ball rotational connections, particularly four-point bearings, have bores through which the raceway system can be filled with rolling elements, particularly ball rolling elements. The bores are provided with and sealed by suitably fitted fill plugs that match the diameter of the bores. Thus, the region of the filling bore and of the associated fill plug also constitutes a weak point in the raceway system, since the load capacity of the raceway section is lower in this region than in the hardened sections of the raceway.
JP 11 248 726 A discloses such a region of a filling bore, which normally is not hardened, as a result of which the load capacity in that region of the raceway is lower than in the hardened raceway sections.
If induction hardening were also performed in the region of the filling bore, this would cause significant geometric “distortion” due to the effect of the heat and the ensuing structural change. The dedicated and precision-fitted fill plugs might then be difficult, or impossible, to insert properly into the hole of the filling bore. For this reason, usually no hardening whatsoever is done in the region of the filling bore(s).
In practice, an attempt is made to palliate both of the above disadvantages by placing the locations of the hardness gap and the bores for feeding the rolling elements into and removing them from the raceway system close together, so that there is only one location in the raceway system where the load capacity is low, instead of two such locations. In practice with regard to ball rotational connections, for example in the case of four-point bearings, the location of the hardness gap is thus also characterized by the fill plug for a bore through which the rolling elements are pushed as they are fed into and removed from the raceway system. This bore usually has a slightly larger cross section than the rolling elements of the raceway system itself. In some rolling bearing arrangements, for example in roller rotational connections, no such filling bores are needed.
In practice and according to the prior art, this region of the hardness gap follows an imaginary line that extends in a radial plane emanating from the axis of rotation of the rotational connection. The region of the hardness gap therefore marks the beginning and the end of the hardened region of a rolling bearing ring.
In all the currently used systems for preferably inductively heating subregions of an annular workpiece, and also in all the abovementioned systems for the, in particular, inductive heating of the rolling element raceways of a rolling bearing ring, the at least one inductor, or induction head, is disposed perpendicular to the rolling element raceway to be hardened, thus resulting in a hardness gap region that extends almost exactly radially to the raceway at the beginning and at the end of each inductively hardened zone. The hardness gap region, like the hardened region, forms so as to be offset parallel to the plane through which the inductor, or induction head, passes circularly during the hardening process. Consequently, the hardness gap region and the hardened zone always form on the same workpiece surface/rolling element raceway.
The width b of such a preferably elongated hardness gap region can be between one and more than fifteen millimeters, or in exceptional cases, even much more, sometimes up to 100 or 200 millimeters, and is dependent on the size of the rolling elements, the machine settings, and the operator's handling of the inductive hardening device, or inductive hardening machine. Some inductive hardening machines are equipped with incremental angle encoders, which cause the hardening to begin at, for example, 0°, and end at, for example, 359°, so that the circular segment covered by the inductor or induction head never amounts to a full 360°. It is customary to try to keep this hardness gap region as small as possible, since it represents a region of lower hardness and thus of lower load capacity, and usually is, or has to be, relief-ground. This relief-grinding involves an additional process, thus entailing more expenditure.
One disadvantage of the conventional systems used heretofore for inductive hardening of rolling element rings is that the aforesaid hardness gap region extending almost exactly radially to the raceway behaves negatively in practice, especially as the—usually hardened—rolling elements roll over this hardness gap region. Consequently, rolling bearing rings hardened according to conventional inductive hardening systems are also disadvantageous in the hardness gap region, in comparison to the hardened regions.
In the first place, the load capacity of a rolling bearing ring that has been inductively hardened in a conventional manner is reduced in the region of the hardness gap, compared to the rest of the hardened raceway; second, this hardness gap region is located in a radially outwardly extending plane emanating from the main axis of rotation, so the running behavior of the rolling elements undergoes an abrupt change whenever they roll over the particular location in the rotational connection where the hardness gap is located; and in the third place, this increases the running noise of the rolling bearing arrangement, or rotational connection, as a whole.
From a consideration of these disadvantages comes the problem initiating the invention, that of creating an improved rolling bearing arrangement that exhibits improved running behavior with a simultaneous increase in load capacity in the beginning and end regions of the raceway hardening(s), which hardening(s) is/are limited in the circumferential direction, accompanied at the same time by reduction of the running noise of the rotational connection, or rolling bearing arrangement, in particular as the rolling elements roll over the beginning and ending region of the raceway hardening(s), and particularly as they roll over the respective hardness gap region.